Current magnetic recording read head may include two shields at both sides of the read head. Shield to shield spacing (SSS) of the read head shall generally be smaller than two bits length to avoid reading flux from adjacent transitions. The minimum SSS may be determined by total thickness of the read head multi-layers.
The read head may generally include a seed layer, an anti-ferromagnetic (AFM) layer, a pinned layer (PL), an anti-ferromagnetic coupling (AFC) layer, a reference layer (RL), a spacer layer (SL), a free layer (FL) and a capping layer (CL). The seed layer may be used to develop a suitable lattice structure of read head layers and the AFM layer may be used to pin the PL magnetization by exchange coupling between the AFM layer and the PL. The respective PL, AFC layer and RL may form a synthetic anti-ferromagnetic (SAF) coupling structure. The SAF coupling structure may provide a highly stable unidirectional anisotropy when the PL may be pinned by the AFM layer. The magnetization direction of the RL, which may always be anti-parallel to that of the PL, thus can be fixed in a desired direction against disturbance of any magnetic field. High stability in the SAF structure may have been demonstrated and may be widely employed in today's magnetic recording read head. In order to get a linear response of the read head, the FL may be biased by a pair of permanent magnets (PM) located at both sides of the read head in an across-track direction so that the magnetization easy axis of the FL may be perpendicular to the RL's magnetization. Magnetic thickness (MSPLtPL, MSRLtRL) of the respective PL and the RL, which may be a product of physical thickness (tPL, tRL) and moment (MSPL, MSRL) of a material, may be selected to be almost the same so that net magnetostatic field from the PL and the RL at the FL may be equal to zero, effectively eliminating biasing or shifting from the operating point of the read head. The magnetization pinning direction of the PL and thus the RL may be set through annealing the read head at a temperature higher than blocking temperature (TB) of the AFM layer, then reducing the temperature to a temperature below TB under a magnetic field. The PL magnetization may thus be fixed parallel to an applied field direction during an annealing process. The pinning direction may be either pointed to or away from an air bearing surface (ABS) in a single spin valve.
It may be well established that all these respective layers may be playing their unique roles in read head performance. Since total thickness of these layers may be generally larger than 20 nm in today's technology, linear density of the read head may be limited to a maximum value of about 2540 Kbpi (bits-per-inch).
Differential CPP dual spin valve magnetic recording read head may have been proposed to overcome linear resolution limited by the SSS, as the magnetic recording read head with the differential CPP dual spin valve structure may not require any magnetic shields.
Differential CPP dual spin valve magnetic recording read head may include two spin valves separated by a gap layer. To achieve a differential effect, the magnetization of the reference layer in the two spin valves may have to be aligned in anti-parallel (AP). Some ways may have been proposed to achieve the AP magnetization state of two reference layers. One way may be to grow the two AFM layers at opposite magnetic fields. However, this process may demonstrate difficulty in control of good pinning directions and thus pinning field may be low. Another way may be to use different AFM materials which may have different blocking temperatures. The AP magnetization state of the RL in the two spin valves may be set by heat treatment in one field direction at higher temperatures (>higher TB), then in another opposite field direction at lower temperatures (lower TB<T<higher TB). However, in this case, the two blocking temperatures should be well separated so that no interference may be caused during setting of exchange bias directions of different AFM layers. The issue may be that the lower TB may not be too low to achieve high pinning stability, while the higher TB may not be too high to avoid the diffusion at high temperature annealing. In addition, the two AFM materials shall provide good corrosive resistance and shall be grown on a same lattice structure. As an additional AFM material may be required, this design may increase cost of a sputtering system for deposition of the read head multi-layers.
Therefore, there is a need to provide for an alternative magnetic reader or magnetic recording read head which may overcome or at least alleviate some of the above-mentioned problems.